Hypertension and cardiac failure are both diseases that cannot always be controlled with current medications. With hypertension, any decrease in blood pressure (particularly pulse pressure) is beneficial. Hypertensive and cardiac failure patients possess heightened sympathetic tone (higher basal activity) and chemoreflex (hypoxic, relating to deficiencies of oxygen) response (a reflex initiated by the stimulation of chemoreceptors, which are specialized cells for detecting chemical substances and relaying that information centrally in the nervous system). Other conditions are also associated with heightened sympathetic tone, which can impart extra load on the heart and other organs. Arterial stiffness, directly related to sympathetic activation and blood pressure, is attracting abundant clinical attention presently, and methods which directly reduce it are now a goal in themselves.
Slow breathing improves arterial baroreflex sensitivity and decreases blood pressure in essential hypertension, which continuous positive airway pressure (CPAP) may assist by avoiding nightly repetitive desaturation and arousal. For example, in certain situations slowed breathing, at 6 breaths per minute, has been shown to be beneficial. Slowed breath rate can independently improve sympathovagal balance, of potential benefit to the general population interested in maximizing cardiovascular health or minimizing stress. (“Sympathovagal balance” refers to the autonomic state resulting from both sympathetic and parasympathetic influences; the autonomic nervous system directs all activities of the body that occur without a person's conscious control, such as breathing and food digestion. Typically, it has two parts: the sympathetic division, which is most active in times of stress, and the parasympathetic division, which controls maintenance activities and helps conserve the body's energy.)
Severe chronic obstructive pulmonary disease (COPD, a term referring to two lung diseases, chronic bronchitis and emphysema) is a condition of airway flow limitation, associated with hypercapnia (a condition in which there is too much CO2 in the blood) and hypoxaemia (a condition in which there is too little O2 in the blood), increased respiratory muscle loading, diminished exercise capacity, elevated respiratory rate, etc. Noninvasive positive pressure ventilation (NPPV, delivery of ventilatory support using a mechanical ventilator connected to a mask or mouthpiece) sessions promoting deep and slowed breathing have been shown to be beneficial, possibly due to a lowered effective respiratory impedance, and a deep slow pattern of breathing has been maintained by patients between sessions.
Therapies exist to help train a patient to consciously breathe slowly using acoustic feedback/training. See, for example, the system known as RESPeRATE (http://www.resperate.com/). See also PCT Publication Number WO 2008/021222, which discloses use of a CPAP machine to reduce a patient's breathing rate.
Thus a paced-breathing systems, methods and/or apparatus that achieves sustained target breath rate in a comfortable and/or tolerated fashion are needed. The therapy may be delivered as daytime sessions of prescribed duration and/or as a nocturnal therapy. The therapy goal is to modify breath rate by delivering mechanical ventilation optimized to achieve a rate target, but sympathetic to the response of the patient such that the therapy is well tolerated. In certain embodiments, the goal is to lower rate to a value optimized to suit the patient and/or the pathology. In certain embodiments, the goal may be to reach an optimal rate, possibly higher than the patient's spontaneous rate.